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Fig. 12.7
Ocean fl oor displacement at the 2011 East Japan earthquake (Source: Fujiwara et al.
2011
(modifi ed))
It is clear that the large movement of ocean fl oor around off Miyagi generated the
large tsunami. The maximum ocean fl oor displacement was estimated over 50 m to
cause the large tsunamis at the 2011 East Japan Earthquake (Fig.
12.7
). This means
that seismic energy has been accumulated in the assumed stable sliding zone.
Finally, several seismogenic segments simultaneously ruptured as the one great
earthquake in 2011.
12.3.2
Observation Records of the 2011 East Japan
Earthquake
The offshore tsunami waveforms were obtained by the pressure gauges with cabled
off Kamaishi (Maeda et al.
2011
). Two types of tsunami were seen in the record.
The one was typical tsunami waveform with the long period, and the other one was
rapid increase like a pulse on the typical tsunami. Probably, the tsunami pulse was
generated by the large movement of ocean fl oor off Miyagi (e.g. Satake et al.
2013
).
These tsunamis further increased their amplitudes according as the approaching to
coastal areas around East Japan due to shoaling and bathymetric effects, and coastal
cities were inundated and damaged severely. The real-time offshore records of pres-
sure gauges have the great importance to improve the earthquake and tsunami early
warning systems for the mega thrust earthquakes and tsunamis.
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